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          <h1 class="post-title" itemprop="name headline">接入层进化史的一些思考

              
            
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              <time title="Created: 2019-01-02 22:25:17" itemprop="dateCreated datePublished" datetime="2019-01-02T22:25:17+08:00">2019-01-02</time>
            

            
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        <p><center>接入层的技术演变很有意思，这篇文章就对自己的小小见解做个记录。</center><br><a id="more"></a></p>
<!-- wp:paragraph -->
<p></p><p>2019年的第一天，写点啥呢？其实满脑子的idea，那就花一年时间慢慢写吧，第一篇就先阐述下自己对接入层架构演变的一些个人思考吧。</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:heading -->
<p></p><h2>一、演进过程的思考</h2><br><!-- /wp:heading --><p></p>
<!-- wp:heading {"level":3} -->
<p></p><h3>1、单体架构</h3><br><!-- /wp:heading --><p></p>
<!-- wp:image {"id":252,"width":350,"height":195} -->
<p><figure class="wp-block-image is-resized"><img src="http://blogsource.chenkaikai.com/uploads/2019/01/server01.png" alt class="wp-image-252" width="350" height="195"></figure><br><!-- /wp:image --></p>
<!-- wp:paragraph -->
<p></p><p><strong>过程</strong>：<br>        1）浏览器的请求通过 DNS Server 解析到指定的 IP 地址<br>        2）浏览器通过 IP 地址访问 Web Server</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>缺点</strong>：<br>1）当到达 Web Server 的性能瓶颈时，无法扩容<br>2）当 Web Server 宕机后整个系统就挂了</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:heading {"level":3} -->
<p></p><h3>2、DNS 轮询</h3><br><!-- /wp:heading --><p></p>
<!-- wp:image {"id":253,"width":446,"height":224} -->
<p><figure class="wp-block-image is-resized"><img src="http://blogsource.chenkaikai.com/uploads/2019/01/server02.png" alt class="wp-image-253" width="446" height="224"></figure><br><!-- /wp:image --></p>
<!-- wp:paragraph -->
<p></p><p><strong>说明</strong>：<br>为了解决 Web Server 的性能瓶颈问题，于是进行了横向扩展，于是最简单的 DNS 轮询便派上了用场。</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>过程</strong>：<br>1）浏览器的每次请求通过 DNS Server 会解析到不同的 IP 地址<br>2）浏览器通过不同的 IP 地址访问不同的 Web Server <br></p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>优点</strong>：<br>1）简单并且零成本，只需要增加 DNS Server 的 IP 解析地址即可<br>2）解决了 Web Server 性能瓶颈的问题</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>缺点</strong>：<br>1）暴露了太多的外网 IP<br>2）DNS 的解析需要一定的生效时间<br>3）如果有一台 Web Server 宕了，但是此时的 DNS Server 并不知道，所以会对部分功能模块产生影响</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:heading {"level":3} -->
<p></p><h3>3、反向代理</h3><br><!-- /wp:heading --><p></p>
<!-- wp:image {"id":254,"width":467,"height":306} -->
<p><figure class="wp-block-image is-resized"><img src="http://blogsource.chenkaikai.com/uploads/2019/01/server03.png" alt class="wp-image-254" width="467" height="306"></figure><br><!-- /wp:image --></p>
<!-- wp:paragraph -->
<p></p><p><strong>说明</strong>：<br>中间加了一层反向代理层，以 Nginx 为例，对整个系统性能的提升是很明显的。</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>过程</strong>：<br>1） 浏览器的请求通过 DNS Server 解析到指定的 IP 地址 <br>2）该 IP 地址对应的是反向代理层，此时将请求转发到身后的 Web Server 集群中<br></p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>优点</strong>：<br>1）只需要暴露一个外网 IP 地址即可<br>2）如果有一台 Web Server 宕了，此时 Nginx 就不会将请求转发给这台服务器<br>3）Web Server 扩展变得更加简单</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>缺点</strong>：<br>1）Nginx 变成了单点，如果出故障，则整个服务变得不可用<br>2）因为多了一个请求转发的过程，请求时间略微增大</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:heading {"level":3} -->
<p></p><h3>4、keepalive</h3><br><!-- /wp:heading --><p></p>
<!-- wp:image {"id":255,"width":467,"height":398} -->
<p><figure class="wp-block-image is-resized"><img src="http://blogsource.chenkaikai.com/uploads/2019/01/server04.png" alt class="wp-image-255" width="467" height="398"></figure><br><!-- /wp:image --></p>
<!-- wp:paragraph -->
<p></p><p><strong>说明</strong>：<br>对反向代理层进行改造，新部署一台 Nginx 服务，并使用 keepalive 技术提供相同的虚拟 IP (VIP)，此时保障了 Nginx 的高可用。</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>优点</strong>：<br>1）增加了 Nginx  的高可用性</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>缺点</strong>：<br>1）其实 Nginx 此时还是单点使用，资源占用率只有 50%，存在资源浪费的现象</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:heading {"level":3} -->
<p></p><h3>5、Lvs/F5</h3><br><!-- /wp:heading --><p></p>
<!-- wp:image {"id":256,"width":467,"height":491} -->
<p><figure class="wp-block-image is-resized"><img src="http://blogsource.chenkaikai.com/uploads/2019/01/server05.png" alt class="wp-image-256" width="467" height="491"></figure><br><!-- /wp:image --></p>
<!-- wp:paragraph -->
<p></p><p><strong>说明</strong>：<br>这种方法其实并不是解决 Nginx 的单点问题的，而是解决 Nginx 的性能问题的，因为 Nginx 只是软件层面的反向代理，而使用 Lvs 技术，或者 F5，它是实施在硬件层面的，性能相较于软件层面的 Nginx，抗压能力又上了一个新的台阶。并且几乎已经满足了所有公司的需求。</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:paragraph -->
<p></p><p><strong>缺点</strong>：<br>1）成本变高，F5 需要进行购买<br>2）比如百度、Google 等日PV超级大的系统，瓶颈还是会出现在反向代理层</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:heading {"level":3} -->
<p></p><h3>6、 Lvs/F5 + DNS 轮询</h3><br><!-- /wp:heading --><p></p>
<!-- wp:image {"id":257,"width":721,"height":480} -->
<p><figure class="wp-block-image is-resized"><img src="http://blogsource.chenkaikai.com/uploads/2019/01/server06.png" alt class="wp-image-257" width="721" height="480"></figure><br><!-- /wp:image --></p>
<!-- wp:paragraph -->
<p></p><p><strong>说明</strong>：<br>其实不管是 Nginx 也好，F5 也好，最终都是有性能瓶颈的，最好的解决办法仍然是水平扩展，一台不行我上两台不就好了，两台不行我就上三台，所以最终的方案还是使用 DNS 轮询来解决。</p><br><!-- /wp:paragraph --><p></p>
<!-- wp:heading -->
<p></p><h2>二、总结</h2><br><!-- /wp:heading --><p></p>
<!-- wp:paragraph -->
<p></p><p>1、谈一谈反向代理层：方向代理层是服务端的统一入口，屏蔽了服务端的所有细节，性能很重要<br>2、关于负载均衡：负载均衡的算法多种多样，比如 IP 哈希、轮询、增加权重等<br>3、所有所有的一切，都围绕着很重要的一个点：高可用 <br>4、很多时候问题的解决，还是需要使用到最最基本的技术，所有的轮子都是建立在基础之上的 <br>5、技术永远没有最好，只有更高，更新迭代的速度是很快的，所以我们都需要永远保持一颗对新技术的探索的好奇心 </p><br><!-- /wp:paragraph --><p></p>

      
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        <div style="text-align:center;color: #ccc;font-size:14px;">------ 本文结束 <i class="fa fa-fighter-jet"></i> 感谢阅读 ------</div>
    
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              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#undefined"><span class="nav-number">1.</span> <span class="nav-text">一、演进过程的思考</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.1.</span> <span class="nav-text">1、单体架构</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.2.</span> <span class="nav-text">2、DNS 轮询</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.3.</span> <span class="nav-text">3、反向代理</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.4.</span> <span class="nav-text">4、keepalive</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.5.</span> <span class="nav-text">5、Lvs/F5</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.6.</span> <span class="nav-text">6、 Lvs/F5 + DNS 轮询</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#undefined"><span class="nav-number">2.</span> <span class="nav-text">二、总结</span></a></li></ol></div>
            

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